vodoo-chile

My brother and I took his car to the dyno today and came away a little concerned. His car is a 92 Z with a built 355 (AFR 195's, CC305 w/114 lobe, SLP's, FPR, and minor boltons) with an ATI 12# intercooled SC and custome programming by Ed Wright. His fuel pressure at idle and low RPM is at about 38lbs on FP guage and only goes up to about 40lbs max at 4500-4900 RPM. As soon as the car begins to get into boost, the A/F ratio gets very lean. It starts at 14.8 and goes up to 18.0 by 4100 rpm. We let off at 4500 rpm for fear of damage. RWHP is 210.8 at 3400 rpm and goes up to 258 at 4000 rpm. After that, it goes drastically down hill, dropping to . Is this just the FMU gone bad or could it be the AFPR. I'm not sure of the relationship between the 2 once the car gets into boost. Any and all help would be greatly appreciated. Thanks,

Kyle

vodoo-chile

Any help? Please,

Kyle

Willie

His fuel pressure at idle and low RPM is at about 38lbs on FP guage and only goes up to about 40lbs max at 4500-4900 RPM.

What is your fuel pressure with the vacuum line disconnected? I'm assuming it's around 45 psig?? Also, what size injectors are you using? Do you know your BLM's under normal cruising condition?


As soon as the car begins to get into boost, the A/F ratio gets very lean.

No wonder. Even without an FMU, your fuel pressure should rise linearly with boost; about one pound fuel pressure per pound of boost. And with an FMU, it should rise significantly higher.

Forty pounds max. is way too low!! I suspect your problem is that the fuel pump cannot supply the demand. What pump(s) do you have?

vodoo-chile

I don't know what the BLM's are but he is running 30lb inj. The FP is about 47 psi at idle, bt have not checked in a while. I know the FP should rise fairly linear as RPM goes up but it didn't even do that. So what I am wondering is it the FP regulator or the FMU? He is running the stock in tank and an inline supplied with the SC kit. It was recently checked and a new relay was put in a few days prior. Any ideas? Thanks,

Kyle

Willie

First, fuel pressure is not a function of engine rpm. It is a function of vacuum/boost. BLM's should be close to 128, but only if the Wright EPROM has an injector constant setting of ~30, to match the injectors. Did you get a printout of the EPROM constants with the EPROM? I'm sure Mr. Wright did not supply you with all the charts. The BLM defaults to 128 in the Power Enrichment mode, so it doesn't matter what it is under WOT. However, I'd like to know under normal driving conditions what the BLM's are. This indicates to me how well matched the EPROM is to the car.

To diagnose, I would check the fuel pressure at idle with the vacuum line disconnected. This will be your baseline.

If you have a hand-held vacuum/boost pump, you can use it on the regulator. At idle, apply boost while watching your fuel pressure gauge. If it rises, there is no problem. If you do not have a vacuum/boost pump, disconnect the FMU and run it to about 4-5 pounds of boost. You won't hurt anything by doing this. Note pressure. It should be about 5-psig above your baseline. I do not know how to test an FMU as I don't use one. But I believe these are the first steps I'd perform.

Willie

vodoo-chile

Thanks, Willie. I'll check that on Sunday.

Kyle